The present invention relates to a semiconductor device, more specifically a semiconductor device having a conductor buried in a hole-shaped pattern or a groove-shaped pattern formed in an insulating film, and a method for fabricating the semiconductor device.
As semiconductor devices are larger-scaled and higher integrated, the design rules of interconnections are more shrunk with generations. Conventionally, interconnection layer has been formed by depositing and patterning the interconnection material by lithography and dry etching.
However, this has found technological limitation as the generations advance. As a new process for forming interconnection layer, which takes the place of the conventional interconnection layer forming process, the so-called damascene process, i.e., forming a groove-shaped pattern or a hole-shaped pattern in inter-layer insulating film and then burying interconnection material in the groove or the hole is being used. The damascene process can easily form interconnection layer of low resistance materials, such as copper, etc., which are difficult for reactive etching, and is very effective to form interconnection layer of low resistance having micronized pattern.
The damascene process is used not only in forming the usual interconnection layers, but also in forming various structures. For example, the Laid-open Japanese Patent Application No. 2000-124403 discloses an inductor and the method for fabricating the same fabricated by the damascene process.
Then, a conventional semiconductor device fabricated by the damascene process will be explained by means of a semiconductor device including an inductor. FIGS. 35A and 35B are plan views of the conventional semiconductor device. FIG. 36 is a diagrammatic view of the conventional semiconductor device, which shows the structure thereof. FIG. 36 is the sectional view along the line A-A′ in FIG. 35B.
An etching stopper film 302 and an inter-layer insulating film 304 are formed on a substrate 300. Interconnection groove 308 is formed in the inter-layer insulating film 304 and the etching stopper film 302. An interconnection 314 having a diffusion preventing film 310 and a copper film 312 is formed in the interconnection groove 308.
An etching stopper film 316 and an inter-layer insulating film 318 are formed on the inter-layer insulating film 304 with the interconnection 314 buried in. Groove-shaped via-holes 326 are formed in the inter-layer insulating film 318 and the etching stopper film 316 down to the interconnection 314. An etching stopper film 320 and an inter-layer insulating film 322 are formed on the inter-layer insulating film 318. Interconnection groove 332 is formed in the inter-layer insulating film 322 and the etching stopper film 320. An interconnection 338 having a diffusion preventing film 334 and a copper film 336 and connected to the interconnection 314 is formed in the via-holes 326 and the interconnection groove 332.
An etching stopper film 340 and an inter-layer insulating film 342 are formed on the inter-layer insulating film 322 with the interconnection 338 buried in. Groove-shaped via-holes 348 are formed in the inter-layer insulating film 342 and the etching stopper film 340 down to the interconnection 338. An etching stopper film 344 and an inter-layer insulating film 346 are formed on the inter-layer insulating film 342. Interconnection groove 350 is formed in the inter-layer insulating film 346 and the etching stopper film 344. An interconnection 356 having a diffusion preventing film 352 and a copper film 354 and connected to the interconnection 338 is formed in the via-holes 348 and the interconnection groove 350.
As shown in FIG. 35A, the interconnections 314, 338, 356 are formed in a spiral in plane, forming the so-called spiral inductor. As shown in FIG. 35B, the interconnections 338, 356 have via portions buried in a plurality of groove-shaped patterns (the via-holes 326, 348) formed along extending direction of the interconnections 338, 356, and main interconnection portions formed on the via portions. Thus, the via portions buried in the groove-shaped patterns, and a plurality of the interconnection layers are formed, whereby the inductor of low interconnection resistance can be fabricated.
As described above, the interconnections formed of mainly copper are used, and the interconnection layers are laid one on another, whereby the inductor of low interconnection resistance can be formed. On the other hand, the copper interconnection is more corrosive than the conventionally used aluminum interconnection and is difficult for wire bonding unsuitably as an uppermost interconnection layer.
Based on these views, the inventor of the present application has made studies of a new inductor structure that the uppermost interconnection layer is formed of aluminum, and an inductor is formed, including the aluminum interconnection layer. However, it has been found that the inductor including the aluminum interconnection layer has new problems which has not taken place in inductors formed of only copper interconnection layers.
FIG. 37 is the sectional view along the line B-B′ in FIG. 35B. As shown in FIG. 37, when contact plugs 362 each having a barrier metal layer 358 and a tungsten film 360 and buried in the via-holes 348 and, and an interconnection 370 having a layer structure of a titanium nitride film 368/an aluminum film 366/a titanium nitride film 364 and formed on the inter-layer insulating film 342 with the contact plugs 362 buried in are formed in place of the interconnection 356, defective filling of the contact plugs 362 has often taken place at the pattern corners of the via-holes 348 (see the parts A and B in FIG. 37).
When the groove-shaped via-holes 348 are formed adjacent to each other, cracks are often made in the inter-layer insulating film 342 at the pattern corner of the outermost via-hole 348 (see the part C in FIG. 37). Also in the interconnections 338, defective filling of the interconnections 338 has often taken place at the pattern corners of the via-holes 326 (see the part D in FIG. 37).
The defective filling of the contact plugs causes poor coverage of the barrier metal layer or the aluminum film in forming the upper interconnection layer formed thereon, the transfer of steps onto the surface of the interconnection layer formed thereon, etc. (see the parts A, B and E in FIG. 37). Defective formation of the upper interconnection layer causes electrically weak parts in the connections between the contact plug and the interconnection.
Cracks in the inter-layer insulating film are a cause of inducing diffusion of copper from the lower interconnection layer. In the case shown in FIG. 37, the etching stopper film of the diffusion preventing film and the silicon nitride film prohibits the diffusion of copper into the inter-layer insulating film. If cracks are made in the inter-layer insulating film, however, the diffusion prohibiting effect of the diffusion preventing film and the etching stopper film is lowered. Copper, which is easily diffused into silicon oxide film at certain temperatures, is a cause of lowering the breakdown voltage between the interconnections when the interconnection of a different potential is present in its neighborhood. The copper is exposed in the interface at the cracks, which is a cause of poor electromigration immunity when excessive current flows.
The defective filling of the contact plugs is true with contact plugs interconnecting a semiconductor substrate with a first interconnection layer. As exemplified in FIG. 38, in a semiconductor device comprising a silicon substrate 400 having a impurity diffused layer 402 formed therein, insulating films 404, 406, 408, 410 sequentially formed on the silicon substrate 400, contact plugs 16 formed of a barrier metal 412 and a tungsten film 414 buried in the insulating films, and an interconnection 422 formed of a diffusion preventing film 418 and a copper film 420 buried in the insulating films 408, 410, when the contact plugs 416 are formed in groove-shaped via-holes, the same defective filling as that in the parts A and B takes place at the corners of the groove-shaped via-holes.
The problems taking place in the application of the above-described interconnection structure has been explained by means of the inductor. However, the same problems take place in forming structures using the groove-shaped via patterns. For example, in the case that the groove-shaped via patterns are used in a guard ring (also called as a seal ring) for protecting the device from water from the environments, etc., the above-described defect is a cause of degrading the moisture resistance. Especially, the guard ring for a redundant circuit, which encloses a fuse region, cracks very influentially occur inside the chips.